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d="M19,2H5C3.3,2,2,3.3,2,5v14c0,1.7,1.3,3,3,3h14c1.7,0,3-1.3,3-3V5C22,3.3,20.7,2,19,2z M20,19c0,0.6-0.4,1-1,1H5c-0.6,0-1-0.4-1-1V5c0-0.6,0.4-1,1-1h14c0.6,0,1,0.4,1,1V19z"></path><path d="M16,11h-3V8c0-0.6-0.4-1-1-1s-1,0.4-1,1v3H8c-0.6,0-1,0.4-1,1s0.4,1,1,1h3v3c0,0.6,0.4,1,1,1s1-0.4,1-1v-3h3c0.6,0,1-0.4,1-1S16.6,11,16,11z"></path></svg></div></div><div class="items" data-v-6e45c352><!--[--><!--[--><a class="VPLink link link" href="/docs/frontend/js/JavaScript%E7%9A%84%E5%9F%BA%E7%A1%80%E8%AF%AD%E6%B3%95.html" style="padding-left:0px;" tabindex="-1" data-v-70e2cdfb data-v-3c355974><!--[--><span class="link-text" data-v-70e2cdfb>基础语法</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/docs/frontend/js/%E5%88%86%E6%94%AF%E7%BB%93%E6%9E%84.html" style="padding-left:0px;" tabindex="-1" data-v-70e2cdfb data-v-3c355974><!--[--><span class="link-text" data-v-70e2cdfb>分支结构</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/docs/frontend/js/%E5%BE%AA%E7%8E%AF%E7%BB%93%E6%9E%84.html" style="padding-left:0px;" tabindex="-1" data-v-70e2cdfb data-v-3c355974><!--[--><span class="link-text" data-v-70e2cdfb>循环结构</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/docs/frontend/js/%E5%87%BD%E6%95%B0(%E4%B8%8A).html" style="padding-left:0px;" tabindex="-1" data-v-70e2cdfb data-v-3c355974><!--[--><span class="link-text" data-v-70e2cdfb>函数（上）</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/docs/frontend/js/%E5%87%BD%E6%95%B0%EF%BC%88%E4%B8%8B%EF%BC%89.html" style="padding-left:0px;" tabindex="-1" data-v-70e2cdfb data-v-3c355974><!--[--><span class="link-text" data-v-70e2cdfb>函数（下）</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/docs/frontend/js/%E6%95%B0%E7%BB%84.html" style="padding-left:0px;" tabindex="-1" data-v-70e2cdfb data-v-3c355974><!--[--><span class="link-text" data-v-70e2cdfb>数组</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/docs/frontend/js/%E5%AD%97%E7%AC%A6%E4%B8%B2%E7%9A%84%E6%93%8D%E4%BD%9C.html" style="padding-left:0px;" tabindex="-1" data-v-70e2cdfb data-v-3c355974><!--[--><span class="link-text" data-v-70e2cdfb>字符串的操作</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/docs/frontend/js/Math%E5%92%8CDate.html" style="padding-left:0px;" tabindex="-1" data-v-70e2cdfb data-v-3c355974><!--[--><span class="link-text" data-v-70e2cdfb>Math和Date</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/docs/frontend/js/BOM%E5%92%8CDOM%EF%BC%88%E4%B8%8A%EF%BC%89.html" style="padding-left:0px;" tabindex="-1" data-v-70e2cdfb data-v-3c355974><!--[--><span class="link-text" data-v-70e2cdfb>BOM和DOM（上）</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/docs/frontend/js/DOM%EF%BC%88%E4%B8%8B%EF%BC%89.html" style="padding-left:0px;" tabindex="-1" data-v-70e2cdfb data-v-3c355974><!--[--><span class="link-text" data-v-70e2cdfb>DOM（下）</span><!--]--><!----></a><!----><!--]--><!--]--></div></section></div><div class="group" data-v-a186aa16><section class="VPSidebarGroup collapsible collapsed" data-v-a186aa16 data-v-6e45c352><div class="title" role="button" data-v-6e45c352><h2 class="title-text" data-v-6e45c352>千锋线下学习</h2><div class="action" data-v-6e45c352><svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" viewbox="0 0 24 24" class="icon minus" data-v-6e45c352><path d="M19,2H5C3.3,2,2,3.3,2,5v14c0,1.7,1.3,3,3,3h14c1.7,0,3-1.3,3-3V5C22,3.3,20.7,2,19,2zM20,19c0,0.6-0.4,1-1,1H5c-0.6,0-1-0.4-1-1V5c0-0.6,0.4-1,1-1h14c0.6,0,1,0.4,1,1V19z"></path><path d="M16,11H8c-0.6,0-1,0.4-1,1s0.4,1,1,1h8c0.6,0,1-0.4,1-1S16.6,11,16,11z"></path></svg><svg version="1.1" xmlns="http://www.w3.org/2000/svg" viewbox="0 0 24 24" class="icon plus" data-v-6e45c352><path d="M19,2H5C3.3,2,2,3.3,2,5v14c0,1.7,1.3,3,3,3h14c1.7,0,3-1.3,3-3V5C22,3.3,20.7,2,19,2z M20,19c0,0.6-0.4,1-1,1H5c-0.6,0-1-0.4-1-1V5c0-0.6,0.4-1,1-1h14c0.6,0,1,0.4,1,1V19z"></path><path d="M16,11h-3V8c0-0.6-0.4-1-1-1s-1,0.4-1,1v3H8c-0.6,0-1,0.4-1,1s0.4,1,1,1h3v3c0,0.6,0.4,1,1,1s1-0.4,1-1v-3h3c0.6,0,1-0.4,1-1S16.6,11,16,11z"></path></svg></div></div><div class="items" data-v-6e45c352><!--[--><!--[--><a class="VPLink link link" href="/docs/frontend/qf/JS%E8%BF%90%E7%AE%97%E7%AC%A6.html" style="padding-left:0px;" tabindex="-1" data-v-70e2cdfb data-v-3c355974><!--[--><span class="link-text" data-v-70e2cdfb>JS运算符</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/docs/frontend/qf/JS%E5%BE%AA%E7%8E%AF%E5%AF%B9%E8%B1%A1.html" style="padding-left:0px;" tabindex="-1" data-v-70e2cdfb data-v-3c355974><!--[--><span class="link-text" data-v-70e2cdfb>JS循环对象</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/docs/frontend/qf/JS%E5%87%BD%E6%95%B0.html" style="padding-left:0px;" tabindex="-1" data-v-70e2cdfb data-v-3c355974><!--[--><span class="link-text" data-v-70e2cdfb>JS函数</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/docs/frontend/qf/JS%E5%AF%B9%E8%B1%A1.html" style="padding-left:0px;" tabindex="-1" data-v-70e2cdfb data-v-3c355974><!--[--><span class="link-text" data-v-70e2cdfb>JS对象</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/docs/frontend/qf/JS%E6%95%B0%E7%BB%84%E9%87%8D%E6%9E%84.html" style="padding-left:0px;" tabindex="-1" data-v-70e2cdfb data-v-3c355974><!--[--><span class="link-text" data-v-70e2cdfb>JS数组重构</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/docs/frontend/qf/JS%E6%95%B0%E7%BB%84%E9%87%8D%E6%9E%842.html" style="padding-left:0px;" tabindex="-1" data-v-70e2cdfb data-v-3c355974><!--[--><span class="link-text" data-v-70e2cdfb>JS数组重构2</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/docs/frontend/qf/JS%E8%B7%AF%E7%94%B1.html" style="padding-left:0px;" tabindex="-1" data-v-70e2cdfb data-v-3c355974><!--[--><span class="link-text" data-v-70e2cdfb>JS路由</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/docs/frontend/qf/JSDOM.html" style="padding-left:0px;" tabindex="-1" data-v-70e2cdfb data-v-3c355974><!--[--><span class="link-text" data-v-70e2cdfb>JSDOM知识</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/docs/frontend/qf/JS%E4%BA%8B%E4%BB%B6.html" style="padding-left:0px;" tabindex="-1" data-v-70e2cdfb data-v-3c355974><!--[--><span class="link-text" data-v-70e2cdfb>JS事件</span><!--]--><!----></a><!----><!--]--><!--]--></div></section></div><!--]--><!--[--><!--]--></nav></aside><div class="VPContent has-sidebar" id="VPContent" data-v-5211c0b1 data-v-296cfad2><div class="VPDoc has-sidebar has-aside" data-v-296cfad2 data-v-cfb513e0><div class="container" data-v-cfb513e0><div class="aside" data-v-cfb513e0><div class="aside-curtain" data-v-cfb513e0></div><div class="aside-container" data-v-cfb513e0><div class="aside-content" data-v-cfb513e0><div class="VPDocAside" data-v-cfb513e0 data-v-afc4c1a1><!--[--><!--]--><!--[--><!--]--><div class="VPDocAsideOutline" data-v-afc4c1a1 data-v-2865c0b0><div class="content" data-v-2865c0b0><div class="outline-marker" data-v-2865c0b0></div><div class="outline-title" data-v-2865c0b0>On this page</div><nav aria-labelledby="doc-outline-aria-label" data-v-2865c0b0><span class="visually-hidden" id="doc-outline-aria-label" data-v-2865c0b0> Table of Contents for current page </span><ul class="root" data-v-2865c0b0 data-v-1188541a><!--[--><!--]--></ul></nav></div></div><!--[--><!--]--><div class="spacer" data-v-afc4c1a1></div><!--[--><!--]--><!----><!--[--><!--]--><!--[--><!--]--></div></div></div></div><div class="content" data-v-cfb513e0><div class="content-container" data-v-cfb513e0><!--[--><!--]--><main class="main" data-v-cfb513e0><div style="position:relative;" class="vp-doc _docs_frontend_qf_JS%E8%BF%90%E7%AE%97%E7%AC%A6" data-v-cfb513e0><div><h2 id="预习整理资料" tabindex="-1">预习整理资料 <a class="header-anchor" href="#预习整理资料" aria-hidden="true">#</a></h2><h4 id="if语句的细节补充" tabindex="-1">if语句的细节补充 <a class="header-anchor" href="#if语句的细节补充" aria-hidden="true">#</a></h4><ol><li>补充一：如果代码块中只有一行代码，那么{}可以省略</li><li>补充二：if(...)语句会计算圆括号内的表达式，并将计算结果转换为布尔型（Boolean） <ul><li>转换规则和Boolean函数的规则一致</li><li><!---->都会被转换成<code>false</code><ul><li>因为它们被称为 “假值”</li></ul></li><li><!---->被转换为`true`,所以它们被称为<!----></li></ul></li></ol><h4 id="逻辑与或的规则" tabindex="-1">逻辑与或的规则 <a class="header-anchor" href="#逻辑与或的规则" aria-hidden="true">#</a></h4><ol><li>逻辑与符号：&amp;&amp;：</li></ol><ul><li><p>只要“&amp;&amp;”前面的逻辑结果是false，无论“&amp;&amp;”后面怎么样，都返回“&amp;&amp;”前面的表达式;</p></li><li><p>只要“&amp;&amp;”前面的逻辑结果是true，无论“&amp;&amp;”后面怎么样，返回“&amp;&amp;”后面的表达式;</p></li></ul><ol start="2"><li>逻辑或符号：||</li></ol><ul><li><p>只要“||”前面的逻辑结果是false，无论“||”后面怎么样，都返回“||”后面的表达式。</p></li><li><p>只要“||”前面的逻辑结果是true，无论“||”后面怎么样，都返回“||”前面的表达式。</p></li></ul><blockquote><ul><li>依靠<code>第一个</code>运算数，就能得出整个运算的逻辑结果，则<code>返回第一个表达式</code> 依靠<code>第二个</code>运算数，才能得出整个运算的逻辑结果，则<code>返回第二个表达式</code></li></ul></blockquote><h2 id="上课资料" tabindex="-1">上课资料 <a class="header-anchor" href="#上课资料" aria-hidden="true">#</a></h2><h4 id="数据类型转换" tabindex="-1">数据类型转换 <a class="header-anchor" href="#数据类型转换" aria-hidden="true">#</a></h4><ol><li><p>任何类型转换为字符串</p><ol><li><p>string() 构造函数转换方式</p><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#FFCB6B;">eg</span><span style="color:#89DDFF;">:</span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#F78C6C;">1</span></span>
<span class="line"><span style="color:#A6ACCD;">	a</span><span style="color:#89DDFF;">=</span><span style="color:#82AAFF;">String</span><span style="color:#A6ACCD;">(a)</span></span>
<span class="line"><span style="color:#A6ACCD;">	</span></span>
<span class="line"><span style="color:#A6ACCD;">	，	</span><span style="color:#676E95;font-style:italic;">// 对象调用String()强转, [object,object]任何对象强转后都是这个字符串</span></span>
<span class="line"><span style="color:#A6ACCD;">   </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;">[</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">,</span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">,</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">,</span><span style="color:#F78C6C;">4</span><span style="color:#A6ACCD;">]	 </span><span style="color:#676E95;font-style:italic;">//调用了数组的一个方法join &quot;1,2,3,4&quot;;  []强转字符串后 &quot;&quot;  [元素] 强转后就会变成这个元素的强字符串&quot;元素&quot;</span></span>
<span class="line"><span style="color:#A6ACCD;">   </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;">[</span><span style="color:#89DDFF;">{</span><span style="color:#F07178;">a</span><span style="color:#89DDFF;">:</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">,</span><span style="color:#F07178;">b</span><span style="color:#89DDFF;">:</span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">}</span><span style="color:#A6ACCD;">]	</span><span style="color:#676E95;font-style:italic;">// [object,object]</span></span>
<span class="line"><span style="color:#A6ACCD;">   </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a				</span><span style="color:#676E95;font-style:italic;">// undefined</span></span>
<span class="line"><span style="color:#A6ACCD;">   </span><span style="color:#C792EA;">function</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">a</span><span style="color:#89DDFF;">(){</span><span style="color:#F07178;">		</span><span style="color:#676E95;font-style:italic;">// 函数会变成字符串函数</span></span>
<span class="line"><span style="color:#F07178;">       </span></span>
<span class="line"><span style="color:#F07178;">   </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#A6ACCD;">	</span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#F78C6C;">464313433434354348483438</span><span style="color:#C792EA;">n</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">// 大整型去除n变成字符串</span></span>
<span class="line"><span style="color:#A6ACCD;">   </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#82AAFF;">Symbol</span><span style="color:#A6ACCD;">()		</span><span style="color:#676E95;font-style:italic;">// &quot;Symbol()&quot;</span></span>
<span class="line"><span style="color:#A6ACCD;">   a</span><span style="color:#89DDFF;">=</span><span style="color:#82AAFF;">String</span><span style="color:#A6ACCD;">(a)  </span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br></div></div><blockquote><p>所有的隐士转换都是强转,也就是该方式</p></blockquote></li><li><p>number转换字符串 toSting() toFixed() <strong>新增拓展方法</strong></p><ul><li><p>toString()</p><div class="language-javascript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">javascript</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#F78C6C;">15</span></span>
<span class="line"><span style="color:#676E95;font-style:italic;">// a.toString(进制转换)  将数值按照指定的进制转换字符串 2-36</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(a</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">toString</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">16</span><span style="color:#A6ACCD;">))	</span><span style="color:#676E95;font-style:italic;">// F</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(a</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">toString</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">2</span><span style="color:#A6ACCD;">))	</span><span style="color:#676E95;font-style:italic;">// 1111</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(a</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">toString</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">10</span><span style="color:#A6ACCD;">))	</span><span style="color:#676E95;font-style:italic;">// 15	如果不写参数,默认是十进制	</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(a</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">toString</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">36</span><span style="color:#A6ACCD;">))	</span><span style="color:#676E95;font-style:italic;">// f</span></span>
<span class="line"></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(a</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">toString</span><span style="color:#A6ACCD;">(几位小数))	</span><span style="color:#676E95;font-style:italic;">// 保留几位小数,会四舍五入</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><blockquote><ul><li>所有的数值是不能直接调用方法的,</li><li>可以存储为变量,让变量调用方法,可以转换为数值型对象调用方法</li></ul></blockquote><ul><li><p>toFixed()</p><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(a</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">toFixed</span><span style="color:#A6ACCD;">(几位小数))	</span><span style="color:#676E95;font-style:italic;">// 保留小数会四舍五入</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(a</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">toPrecision</span><span style="color:#A6ACCD;">(保留几位))	</span><span style="color:#676E95;font-style:italic;">// 四舍五入做科学计数法,如果是小数,保留数值位数,不做四舍五入,不用科学计数法;范围1-21</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(a</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">toExponential</span><span style="color:#A6ACCD;">(小数点后的位数))	</span><span style="color:#676E95;font-style:italic;">// 科学技术法表示,保留小数后位数,会自动四舍五入</span></span>
<span class="line"><span style="color:#A6ACCD;">a</span><span style="color:#89DDFF;">=</span><span style="color:#F78C6C;">34.567</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(a</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">toFixed</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">2</span><span style="color:#A6ACCD;">))</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div></li></ul></li></ul></li><li><p>对象和数组 toString() <strong>基础方法</strong></p></li></ol></li><li><p>任何类型转换数值</p><ol><li><p>Number() 强转换 数值类型中包括两种,一个是数值,一个是Nan(非数值)</p><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">3a</span><span style="color:#89DDFF;">&quot;</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">//nan</span></span>
<span class="line"><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=null</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">// nan</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#82AAFF;">Number</span><span style="color:#A6ACCD;">(</span><span style="color:#C792EA;">function</span><span style="color:#89DDFF;">(){}</span><span style="color:#A6ACCD;">))</span></span>
<span class="line"></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><blockquote><ul><li><p>无其他字符的纯数值字符串转换为数值,null转换为数值0,可以将布尔值true转换1,false转换为0</p></li><li><p>可以将空数组转换为0,可以将这个一个数值元素或者一个纯数值字符串元素转换为数值</p></li><li><p>bigInt会转换为数值</p></li><li><p>其他任何内容转换为数值均为NaN</p></li></ul></blockquote></li><li><p>字符串转换为数值</p><ol><li><p>全局方法</p><ul><li>parseInt(要转的元素,进制) 转换为整数 将第一个参数隐士转换为字符串后再转换为整数</li><li>ParseFloat() 转换为浮点型</li></ul></li><li><p>都会转换为10进制,如果没有进制,默认转换为10进制,并且将不符合的内容去掉</p><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#82AAFF;">parseInt</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">FF</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">,</span><span style="color:#F78C6C;">16</span><span style="color:#A6ACCD;">))</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#82AAFF;">parseInt</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">101110101</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">,</span><span style="color:#F78C6C;">2</span><span style="color:#A6ACCD;">))</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#82AAFF;">parseInt</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">10151</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">,</span><span style="color:#F78C6C;">2</span><span style="color:#A6ACCD;">))	</span><span style="color:#676E95;font-style:italic;">// 5</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#82AAFF;">parseFloat</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">2.2.5</span><span style="color:#89DDFF;">&quot;</span><span style="color:#A6ACCD;">))	</span><span style="color:#676E95;font-style:italic;">// 2.2</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#82AAFF;">parseFloat</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">3a</span><span style="color:#89DDFF;">&quot;</span><span style="color:#A6ACCD;">))	</span><span style="color:#676E95;font-style:italic;">// 不能使用进制,小数点运算进制是有问题</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div></li></ol></li></ol></li><li><p>任何类型转换为布尔值</p><ol><li>Boolean() 强转布尔值 <ul><li>&quot;&quot; , false , 0, undefined, null , Nan 均为false(0),其他都是1</li></ul></li><li>遇到任何数组转换布尔值时,不会优先转换为字符串再转布尔,而是直接转换为布尔True</li></ol></li><li><p>强转对象</p><ol><li>object() 只要使用object强转都会变为引用类型</li></ol><blockquote><p>javascript中的引用类型有：</p><p>1.object，对象；</p><p>2.Array，数组；</p><p>3.Function，函数；</p><p>4.Date，日期时间类型；</p><p>5.RegExp，正则表达式</p></blockquote></li></ol><p>​</p><h4 id="运算" tabindex="-1">运算 <a class="header-anchor" href="#运算" aria-hidden="true">#</a></h4><ol><li><p>数值运算</p><ol><li><p>非数值加法运算(+)</p><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">+</span><span style="color:#FF9CAC;">true</span><span style="color:#A6ACCD;">)	</span><span style="color:#676E95;font-style:italic;">// number+boolean	boolean隐士转换数值</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">+undefined</span><span style="color:#A6ACCD;">)	</span><span style="color:#676E95;font-style:italic;">// number+undefined	undefined隐士转换数值Nan</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">+null</span><span style="color:#A6ACCD;">)		</span><span style="color:#676E95;font-style:italic;">// 3 null隐士转换数值为0</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">+{</span><span style="color:#F07178;">a</span><span style="color:#89DDFF;">:</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">}</span><span style="color:#A6ACCD;">)	</span><span style="color:#676E95;font-style:italic;">// 对象会隐士转换为字符串,数值和对象字符串首尾相连</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;">[</span><span style="color:#F78C6C;">2</span><span style="color:#A6ACCD;">])		</span><span style="color:#676E95;font-style:italic;">// 将数组转换为字符串,首尾相连</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">0</span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;">[])		</span><span style="color:#676E95;font-style:italic;">// 0+&#39;0&#39;</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">+</span><span style="color:#F78C6C;">45879586562</span><span style="color:#C792EA;">n</span><span style="color:#A6ACCD;">)		</span><span style="color:#676E95;font-style:italic;">// 错误,无法相加</span></span>
<span class="line"></span>
<span class="line"></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">3</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">+</span><span style="color:#FF9CAC;">true</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// string+任何类型  都会将后面的类型隐士转换为字符串然后拼接</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">a</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">+{</span><span style="color:#F07178;">a</span><span style="color:#89DDFF;">:</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">}</span><span style="color:#A6ACCD;">)	</span><span style="color:#676E95;font-style:italic;">// a[object object]</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">a</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;">[</span><span style="color:#F78C6C;">1</span><span style="color:#A6ACCD;">])	</span><span style="color:#676E95;font-style:italic;">// &quot;a1&quot;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#FF9CAC;">false</span><span style="color:#89DDFF;">+</span><span style="color:#FF9CAC;">true</span><span style="color:#A6ACCD;">)		</span><span style="color:#676E95;font-style:italic;">// 数值相加</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">{</span><span style="color:#F07178;">a</span><span style="color:#89DDFF;">:</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">,</span><span style="color:#F07178;">b</span><span style="color:#89DDFF;">:</span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">}+</span><span style="color:#FF9CAC;">true</span><span style="color:#A6ACCD;">)		</span><span style="color:#676E95;font-style:italic;">// 对象和数组都会隐士转换为字符串相加</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">undefined+</span><span style="color:#FF9CAC;">true</span><span style="color:#A6ACCD;">)	</span><span style="color:#676E95;font-style:italic;">// undefined和null遇到布尔值相加都会转换为数值</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">([</span><span style="color:#F78C6C;">1</span><span style="color:#A6ACCD;">]</span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;">[</span><span style="color:#F78C6C;">2</span><span style="color:#A6ACCD;">])	</span><span style="color:#676E95;font-style:italic;">// 12</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br></div></div></li><li><p>所有的 - * / % 都会隐士转换为数值运算</p><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">45</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">-</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">2</span><span style="color:#89DDFF;">&quot;</span><span style="color:#A6ACCD;">)	</span><span style="color:#676E95;font-style:italic;">// 43</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">([]</span><span style="color:#89DDFF;">-</span><span style="color:#A6ACCD;">[])		</span><span style="color:#676E95;font-style:italic;">// 0</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">45</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">-</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">null</span><span style="color:#A6ACCD;">)	</span><span style="color:#676E95;font-style:italic;">// 45</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div></li><li><p>** 求幂</p><blockquote><p>进制使用 ** 立方根求值</p></blockquote><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">**</span><span style="color:#F78C6C;">2</span><span style="color:#A6ACCD;">)	</span><span style="color:#676E95;font-style:italic;">// 9</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">9</span><span style="color:#89DDFF;">**</span><span style="color:#F78C6C;">0.5</span><span style="color:#A6ACCD;">)	</span><span style="color:#676E95;font-style:italic;">// 3</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div></li></ol></li><li><p>赋值运算符和一元运算符</p><ol><li><p>赋值运算符</p><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">a</span><span style="color:#89DDFF;">+=</span><span style="color:#F78C6C;">2</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">// 5</span></span>
<span class="line"><span style="color:#A6ACCD;">a</span><span style="color:#89DDFF;">+=</span><span style="color:#89DDFF;">&quot;&quot;</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">// 3</span></span>
<span class="line"><span style="color:#A6ACCD;">a</span><span style="color:#89DDFF;">+=</span><span style="color:#A6ACCD;">[</span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;">]	</span><span style="color:#676E95;font-style:italic;">// 33</span></span>
<span class="line"><span style="color:#A6ACCD;">a</span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;">a</span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;">[</span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;">]	</span><span style="color:#676E95;font-style:italic;">// 33</span></span>
<span class="line"><span style="color:#A6ACCD;">赋值运算符运算依照 </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">-</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">*</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">/</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">%</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">**</span><span style="color:#A6ACCD;"> 运算符</span></span>
<span class="line"></span>
<span class="line"><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">5.23</span><span style="color:#89DDFF;">&quot;</span></span>
<span class="line"><span style="color:#A6ACCD;">a</span><span style="color:#89DDFF;">-=</span><span style="color:#F78C6C;">0</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">// 5.23</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div></li><li><p>一元运算符</p><blockquote><p>a++ a-- ++a --a</p></blockquote><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">3</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> b </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> a </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">5</span></span>
<span class="line"><span style="color:#A6ACCD;">        console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(a</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> b)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">  </span><span style="color:#676E95;font-style:italic;">// 5,5</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> obj </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span><span style="color:#A6ACCD;"> </span><span style="color:#F07178;">a</span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">1</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#A6ACCD;">        obj </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> obj</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">a </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span><span style="color:#A6ACCD;"> </span><span style="color:#F07178;">b</span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">10</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#A6ACCD;">        console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(obj)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">   </span><span style="color:#676E95;font-style:italic;">// { b: 10 }</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> obj </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span><span style="color:#A6ACCD;"> </span><span style="color:#F07178;">a</span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">1</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> o </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> obj</span></span>
<span class="line"><span style="color:#A6ACCD;">        obj</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">a </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> obj </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span><span style="color:#A6ACCD;"> </span><span style="color:#F07178;">b</span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">10</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#A6ACCD;">        console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(obj)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">   </span><span style="color:#676E95;font-style:italic;">// { b: 10 }</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#676E95;font-style:italic;">// 定义变量</span></span>
<span class="line"><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;">b</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;">c</span></span>
<span class="line"><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a1</span><span style="color:#89DDFF;">=</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">,</span></span>
<span class="line"><span style="color:#A6ACCD;">	b1</span><span style="color:#89DDFF;">=</span><span style="color:#F78C6C;">4</span><span style="color:#89DDFF;">,</span></span>
<span class="line"><span style="color:#A6ACCD;">	b1</span><span style="color:#89DDFF;">=</span><span style="color:#F78C6C;">5</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a2</span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;">b2</span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;">c2</span><span style="color:#89DDFF;">=</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">// 3 3 3</span></span>
<span class="line"></span>
<span class="line"></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#89DDFF;">        </span><span style="color:#676E95;font-style:italic;">// 优先级 赋值运算*=  =优先级很低</span></span>
<span class="line"><span style="color:#A6ACCD;">		</span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2</span></span>
<span class="line"><span style="color:#A6ACCD;">        a </span><span style="color:#89DDFF;">*=</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">3</span></span>
<span class="line"><span style="color:#A6ACCD;">        console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(a)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;"> </span><span style="color:#676E95;font-style:italic;">// 10</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#89DDFF;">        </span><span style="color:#676E95;font-style:italic;">// 赋值运算符要是计算不了,就先进行加减计算</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">3</span></span>
<span class="line"><span style="color:#A6ACCD;">        a </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> a </span><span style="color:#89DDFF;">+=</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2</span><span style="color:#A6ACCD;">  </span><span style="color:#676E95;font-style:italic;">// 5</span></span>
<span class="line"><span style="color:#A6ACCD;">        a </span><span style="color:#89DDFF;">+=</span><span style="color:#A6ACCD;"> a </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">4</span><span style="color:#A6ACCD;">  </span><span style="color:#676E95;font-style:italic;">// 7</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#89DDFF;">        </span><span style="color:#676E95;font-style:italic;">// 任何一元运算符，计算时都会隐式转换为数值运算</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">1</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">        a</span><span style="color:#89DDFF;">++</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">// 2</span></span>
<span class="line"></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;">[]</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">        a</span><span style="color:#89DDFF;">++;</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">// 1</span></span>
<span class="line"></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;">[</span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;">]</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">        a</span><span style="color:#89DDFF;">++;</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">// 4</span></span>
<span class="line"><span style="color:#A6ACCD;">        console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(a)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br></div></div><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">		</span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">             </span><span style="color:#F78C6C;">2</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">4</span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;">  </span><span style="color:#F78C6C;">4</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">+</span><span style="color:#F78C6C;">5</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">+</span><span style="color:#F78C6C;">5</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">+</span><span style="color:#F78C6C;">6</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> s</span><span style="color:#89DDFF;">=++</span><span style="color:#A6ACCD;">a </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">++</span><span style="color:#A6ACCD;">a </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">++</span><span style="color:#A6ACCD;">a </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">++</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;">a </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">++</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">            console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(s</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;">a)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#89DDFF;">            </span><span style="color:#676E95;font-style:italic;">// ++ -- 一元运算的优先级高于+ - * /</span></span>
<span class="line"></span>
<span class="line"><span style="color:#A6ACCD;">            </span><span style="color:#89DDFF;font-style:italic;">for</span><span style="color:#A6ACCD;">(</span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> i</span><span style="color:#89DDFF;">=</span><span style="color:#F78C6C;">10</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">i</span><span style="color:#89DDFF;">--;</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">               </span><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#F07178;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">aa</span><span style="color:#89DDFF;">&quot;</span><span style="color:#F07178;">)</span></span>
<span class="line"><span style="color:#F07178;">            </span><span style="color:#89DDFF;">}</span></span>
<span class="line"></span>
<span class="line"><span style="color:#A6ACCD;">            </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> arr</span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;">[</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">,</span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">,</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">,</span><span style="color:#F78C6C;">4</span><span style="color:#89DDFF;">,</span><span style="color:#F78C6C;">5</span><span style="color:#A6ACCD;">]</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">            </span><span style="color:#89DDFF;font-style:italic;">for</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">arr</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">length</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">arr</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">length</span><span style="color:#89DDFF;">--</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">                </span><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#F07178;">(</span><span style="color:#A6ACCD;">arr</span><span style="color:#F07178;">[</span><span style="color:#A6ACCD;">arr</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">length</span><span style="color:#89DDFF;">-</span><span style="color:#F78C6C;">1</span><span style="color:#F07178;">])</span></span>
<span class="line"><span style="color:#F07178;">            </span><span style="color:#89DDFF;">}</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br></div></div></li><li><p>关系运算符</p><ul><li>关系运算符返回一个布尔值</li><li>&lt; &gt; &lt;= &gt;= == === <code>!==</code> <code>!===</code></li><li>ASCII utf-8 Unicode(万国码)</li></ul><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">aa</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> b</span><span style="color:#89DDFF;">=</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">ab</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">        console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(b</span><span style="color:#89DDFF;">&gt;</span><span style="color:#A6ACCD;">a)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#A6ACCD;">        console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">谢</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">&gt;</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">一</span><span style="color:#89DDFF;">&quot;</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"></span>
<span class="line"><span style="color:#A6ACCD;">        console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">&gt;</span><span style="color:#F78C6C;">4</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"><span style="color:#A6ACCD;">        console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">1.2</span><span style="color:#89DDFF;">&lt;</span><span style="color:#F78C6C;">1.1999</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"></span>
<span class="line"><span style="color:#A6ACCD;">        console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#FF9CAC;">true</span><span style="color:#89DDFF;">&gt;</span><span style="color:#F78C6C;">1</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#676E95;font-style:italic;">//隐式转换为数值  false</span></span>
<span class="line"><span style="color:#A6ACCD;">        console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">undefined&gt;null</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">//false</span></span>
<span class="line"><span style="color:#A6ACCD;">        console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">null&gt;undefined</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">//false</span></span>
<span class="line"><span style="color:#A6ACCD;">        console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">{</span><span style="color:#F07178;">a</span><span style="color:#89DDFF;">:</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">}&lt;{</span><span style="color:#F07178;">a</span><span style="color:#89DDFF;">:</span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">}</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">//false</span></span>
<span class="line"><span style="color:#A6ACCD;">        console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">([</span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;">]</span><span style="color:#89DDFF;">&lt;</span><span style="color:#A6ACCD;">[</span><span style="color:#F78C6C;">4</span><span style="color:#A6ACCD;">])			</span><span style="color:#676E95;font-style:italic;">//true</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br></div></div><ul><li><code>==</code> 先隐士转换为相同类型,在比较</li><li><code>===</code> 绝对比较 先比较类型,再比较值</li></ul><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#676E95;font-style:italic;">// 三个完全相互相等</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;&quot;</span><span style="color:#89DDFF;">==</span><span style="color:#FF9CAC;">false</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">// true</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#FF9CAC;">false</span><span style="color:#89DDFF;">==</span><span style="color:#F78C6C;">0</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">// true</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;&quot;</span><span style="color:#89DDFF;">==</span><span style="color:#F78C6C;">0</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">// true</span></span>
<span class="line"></span>
<span class="line"><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;">[]</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;">[</span><span style="color:#89DDFF;">&quot;&quot;</span><span style="color:#A6ACCD;">]</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;">[</span><span style="color:#F78C6C;">0</span><span style="color:#A6ACCD;">]</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#676E95;font-style:italic;">// 六个可以进入条件 (number,string,undefined,null,bigint,object)</span></span>
<span class="line"><span style="color:#89DDFF;font-style:italic;">if</span><span style="color:#A6ACCD;">(a</span><span style="color:#89DDFF;">==</span><span style="color:#F78C6C;">0</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">	</span><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#F07178;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">aaa</span><span style="color:#89DDFF;">&quot;</span><span style="color:#F07178;">)</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br></div></div><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#89DDFF;">        </span><span style="color:#676E95;font-style:italic;">// 任何值与NaN都不相同</span></span>
<span class="line"><span style="color:#A6ACCD;">        console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">NaN==NaN</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#676E95;font-style:italic;">//false</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">a</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#89DDFF;">        </span><span style="color:#676E95;font-style:italic;">// isNaN，先隐式转换为数值，然后判断是不是NaN</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#89DDFF;font-style:italic;">if</span><span style="color:#A6ACCD;">(</span><span style="color:#82AAFF;">isNaN</span><span style="color:#A6ACCD;">(a))</span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">            </span><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#F07178;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">aaa</span><span style="color:#89DDFF;">&quot;</span><span style="color:#F07178;">)</span></span>
<span class="line"><span style="color:#F07178;">        </span><span style="color:#89DDFF;">}</span></span>
<span class="line"></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#89DDFF;">        </span><span style="color:#676E95;font-style:italic;">// 不隐式转换为数值，直接判断是否是NaN</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#89DDFF;font-style:italic;">if</span><span style="color:#A6ACCD;">(Number</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">isNaN</span><span style="color:#A6ACCD;">(a))</span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">            </span><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#F07178;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">aaa</span><span style="color:#89DDFF;">&quot;</span><span style="color:#F07178;">)</span></span>
<span class="line"><span style="color:#F07178;">        </span><span style="color:#89DDFF;">}</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#676E95;font-style:italic;">// console.log([]==[]);//数组是引用类型，两个不同的数组，引用地址不同，false,数据类型相同，所以不隐式转换</span></span>
<span class="line"><span style="color:#89DDFF;">            </span><span style="color:#676E95;font-style:italic;">// console.log([]==&quot;&quot;);</span></span>
<span class="line"><span style="color:#89DDFF;">            </span><span style="color:#676E95;font-style:italic;">// console.log([]==0)</span></span>
<span class="line"><span style="color:#89DDFF;">            </span><span style="color:#676E95;font-style:italic;">// !强制隐式转换为布尔值再取反</span></span>
<span class="line"><span style="color:#89DDFF;">            </span><span style="color:#676E95;font-style:italic;">// console.log([]==![]);//true</span></span>
<span class="line"><span style="color:#89DDFF;">            </span><span style="color:#676E95;font-style:italic;">// console.log([2]==2);</span></span>
<span class="line"><span style="color:#89DDFF;">            </span><span style="color:#676E95;font-style:italic;">// console.log([0]==false)</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div></li><li><p>逻辑运算符</p><ul><li><p>逻辑与运算符概念:</p><ul><li><p>true &amp;&amp; true true</p><p>true &amp;&amp; false false</p><p>false &amp;&amp; true false</p><p>false &amp;&amp; false false</p></li><li><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&amp;&amp;</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">0</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">    </span><span style="color:#676E95;font-style:italic;">// 0</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div></li></ul></li><li><p>逻辑或运算符概念 ||</p><ul><li><p>true || true true</p><p>true || false true</p><p>false || true true</p><p>false || false false</p></li><li><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">0</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">||</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">    </span><span style="color:#676E95;font-style:italic;">// 3</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div></li></ul></li><li><p>! 逻辑非，强制隐式转换为布尔值，并且取反</p><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> o </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">0</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#89DDFF;font-style:italic;">if</span><span style="color:#A6ACCD;"> (o) </span><span style="color:#89DDFF;">{</span></span>
<span class="line"></span>
<span class="line"><span style="color:#F07178;">        </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#89DDFF;font-style:italic;">if</span><span style="color:#A6ACCD;"> (</span><span style="color:#89DDFF;">!</span><span style="color:#A6ACCD;">o) </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">            </span><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#F07178;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">aaa</span><span style="color:#89DDFF;">&#39;</span><span style="color:#F07178;">)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#F07178;">        </span><span style="color:#89DDFF;">}</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div></li></ul></li><li><p>位运算符</p><ol><li><p>二进制</p><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">#FF0000FF </span><span style="color:#82AAFF;">rgba</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">255</span><span style="color:#89DDFF;">,</span><span style="color:#F78C6C;">255</span><span style="color:#89DDFF;">,</span><span style="color:#F78C6C;">255</span><span style="color:#89DDFF;">,</span><span style="color:#F78C6C;">1</span><span style="color:#A6ACCD;">)	</span><span style="color:#F78C6C;">11111111</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div></li><li><p>十进制</p><ul><li>除2取余法</li><li>展开式</li></ul></li><li><p>八进制</p><ul><li>101,011,011 =&gt; 533</li></ul></li><li><p>十六进制</p><ul><li>cd5f =&gt; 1100110101011111</li></ul></li><li><p>&amp;运算符</p><ul><li><p>概念:</p></li><li><p>​ 1&amp;1 1</p><p>​ 1&amp;0 0</p><p>​ 0&amp;1 0</p><p>​ 0&amp;0 0</p></li></ul><div class="language-JavaScript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">JavaScript</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">567</span><span style="color:#89DDFF;">&amp;</span><span style="color:#F78C6C;">15</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"><span style="color:#F78C6C;">567</span><span style="color:#A6ACCD;"> </span><span style="color:#C792EA;">=&gt;</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">110010111</span></span>
<span class="line"><span style="color:#F78C6C;">15</span><span style="color:#A6ACCD;">  </span><span style="color:#C792EA;">=&gt;</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">000001111</span></span>
<span class="line"><span style="color:#A6ACCD;">得出 </span><span style="color:#F78C6C;">000000111</span></span>
<span class="line"><span style="color:#A6ACCD;">得到 </span><span style="color:#F78C6C;">17</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><blockquote><p>注意点:任何数与2的n次幂-1相与,得到的结果是这个数除以2的n次幂的余数</p></blockquote></li><li><p>|位运算符</p><ul><li><p>概念:</p></li><li><p>​ 1|1 1 ​ 0|1 1 ​ 1|1 1 ​ 0|0 0</p></li></ul><div class="language-JavaScript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">JavaScript</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">12</span><span style="color:#89DDFF;">|</span><span style="color:#F78C6C;">14</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"><span style="color:#F78C6C;">12</span><span style="color:#A6ACCD;"> </span><span style="color:#C792EA;">=&gt;</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">1100</span></span>
<span class="line"><span style="color:#F78C6C;">14</span><span style="color:#A6ACCD;">  </span><span style="color:#C792EA;">=&gt;</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">1110</span></span>
<span class="line"><span style="color:#A6ACCD;">得出 </span><span style="color:#F78C6C;">1110</span></span>
<span class="line"><span style="color:#A6ACCD;">得到 </span><span style="color:#F78C6C;">14</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><blockquote><p>注意点: 1. 任何数与2的n次幂-1相或时，得到的结果都是大于等于2的n次幂</p></blockquote><ol start="2"><li>如果这个数小于2的n次幂-1时，值就是2的n次幂-1</li></ol></li><li><p>^ 异或运算</p><ul><li><p>概念:</p></li><li><p>​ <strong>相同为0不同为1</strong> ​ 1^1=0 ​ 1^0=1 ​ 0^1=1 ​ 0^0=1</p></li></ul><div class="language-JavaScript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">JavaScript</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">   异或用于加密和解密</span></span>
<span class="line"><span style="color:#A6ACCD;">   console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">234567</span><span style="color:#89DDFF;">^</span><span style="color:#F78C6C;">987654</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"><span style="color:#A6ACCD;">   console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">820801</span><span style="color:#89DDFF;">^</span><span style="color:#F78C6C;">987654</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div></li><li><p>~ 位非</p><ul><li>概念: +1取负</li></ul><div class="language-JavaScript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">JavaScript</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">   </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">   a</span><span style="color:#89DDFF;">=~</span><span style="color:#A6ACCD;">a</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">   console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(a) </span><span style="color:#676E95;font-style:italic;">//-4</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><div class="language-JavaScript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">JavaScript</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#89DDFF;">   </span><span style="color:#676E95;font-style:italic;">// 取整</span></span>
<span class="line"><span style="color:#A6ACCD;">   </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#F78C6C;">3.21</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">   a</span><span style="color:#89DDFF;">=~~</span><span style="color:#A6ACCD;">a</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">   console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(a)</span></span>
<span class="line"></span>
<span class="line"><span style="color:#89DDFF;">   </span><span style="color:#676E95;font-style:italic;">// 转换为数值并且取整</span></span>
<span class="line"><span style="color:#A6ACCD;">   </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">ab</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">   console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">~~</span><span style="color:#A6ACCD;">a)</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div></li><li><p>右移运算符</p><div class="language-JavaScript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">JavaScript</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">   console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">16</span><span style="color:#89DDFF;">&gt;&gt;</span><span style="color:#F78C6C;">2</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">   </span><span style="color:#F78C6C;">10000</span><span style="color:#89DDFF;">--&gt;</span><span style="color:#F78C6C;">100</span><span style="color:#89DDFF;">--</span><span style="color:#F78C6C;">4</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><div class="language-JavaScript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">JavaScript</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">   console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">&lt;&lt;</span><span style="color:#F78C6C;">6</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">   </span><span style="color:#F78C6C;">11</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">--&gt;</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">11000000</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">--&gt;</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">192</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><div class="language-JavaScript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">JavaScript</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">   console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">&lt;&lt;</span><span style="color:#F78C6C;">6</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">   </span><span style="color:#F78C6C;">10</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">--&gt;</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">10000000</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">--&gt;</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">128</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div></li></ol></li></ol></li></ol><h4 id="三元运算符" tabindex="-1">三元运算符 <a class="header-anchor" href="#三元运算符" aria-hidden="true">#</a></h4><ul><li>三元运算符，如果返回布尔值时，不要三元运算符</li></ul><div class="language-JavaScript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">JavaScript</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">   </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">   </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> b</span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;">a</span><span style="color:#89DDFF;">&gt;</span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">?</span><span style="color:#A6ACCD;"> </span><span style="color:#FF9CAC;">false</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#FF9CAC;">true</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">   </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> b</span><span style="color:#89DDFF;">=!</span><span style="color:#A6ACCD;">(a</span><span style="color:#89DDFF;">&gt;</span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><ul><li>三元运算可以多个连用</li></ul><div class="language-JavaScript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">JavaScript</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">     </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">     </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> b</span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;">a</span><span style="color:#89DDFF;">&gt;</span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">?</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">1</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">===</span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">?</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">0</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">-</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><div class="language-JavaScript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">JavaScript</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">     </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#F78C6C;">4</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">     </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> b</span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;">a</span><span style="color:#89DDFF;">&gt;</span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">?</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">1</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">0</span></span>
<span class="line"><span style="color:#A6ACCD;">     </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> b</span><span style="color:#89DDFF;">=</span><span style="color:#82AAFF;">Number</span><span style="color:#A6ACCD;">(a</span><span style="color:#89DDFF;">&gt;</span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">     </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> b</span><span style="color:#89DDFF;">=~~</span><span style="color:#A6ACCD;">(a</span><span style="color:#89DDFF;">&gt;</span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">     console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(b)  </span><span style="color:#676E95;font-style:italic;">// 1</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><ul><li>三元运算符优先级，优先于赋值运算符</li></ul><div class="language-JavaScript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">JavaScript</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">   </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">   </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> b</span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;">a</span><span style="color:#89DDFF;">+=</span><span style="color:#A6ACCD;">   </span><span style="color:#F78C6C;">1</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">?</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">0</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">// 3</span></span>
<span class="line"><span style="color:#A6ACCD;">   </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> b</span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;">a</span><span style="color:#89DDFF;">+=</span><span style="color:#A6ACCD;">   </span><span style="color:#F78C6C;">0</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">?</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">1</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">// 5</span></span>
<span class="line"><span style="color:#A6ACCD;">   console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(b)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#A6ACCD;">   </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> c </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">245</span></span>
<span class="line"><span style="color:#A6ACCD;">   </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> d </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> c </span><span style="color:#89DDFF;">+=</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">?</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">18</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">10</span></span>
<span class="line"><span style="color:#A6ACCD;">   console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(d)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">// 263</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><h4 id="条件运算符" tabindex="-1">条件运算符 <a class="header-anchor" href="#条件运算符" aria-hidden="true">#</a></h4><ul><li><p>将表达式的结果转换为布尔值,如果是true进入条件,如果是false不执行条件语句</p></li><li><p>条件语句中,只有一句话的时候,可以省略<code>大括号</code>,直接书写即可</p></li><li><p>格式：</p><div class="language-JavaScript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">JavaScript</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#89DDFF;font-style:italic;">if</span><span style="color:#A6ACCD;">(表达式)</span><span style="color:#89DDFF;">{</span></span>
<span class="line"></span>
<span class="line"><span style="color:#F07178;">   </span><span style="color:#89DDFF;">}</span></span>
<span class="line"></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#89DDFF;font-style:italic;">if</span><span style="color:#A6ACCD;">()</span><span style="color:#89DDFF;">{</span></span>
<span class="line"></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">}</span><span style="color:#89DDFF;font-style:italic;">else</span><span style="color:#89DDFF;">{</span></span>
<span class="line"></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">}</span></span>
<span class="line"></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#89DDFF;font-style:italic;">if</span><span style="color:#A6ACCD;">()</span><span style="color:#89DDFF;">{</span></span>
<span class="line"></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">}</span><span style="color:#89DDFF;font-style:italic;">else</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;font-style:italic;">if</span><span style="color:#A6ACCD;">()</span><span style="color:#89DDFF;">{</span></span>
<span class="line"></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">}</span><span style="color:#89DDFF;font-style:italic;">else</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;font-style:italic;">if</span><span style="color:#A6ACCD;">()</span><span style="color:#89DDFF;">{</span></span>
<span class="line"></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">}</span><span style="color:#89DDFF;font-style:italic;">else</span><span style="color:#89DDFF;">{</span></span>
<span class="line"></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">}</span></span>
<span class="line"></span>
<span class="line"><span style="color:#A6ACCD;">     </span><span style="color:#89DDFF;font-style:italic;">if</span><span style="color:#A6ACCD;">()</span><span style="color:#89DDFF;">{</span></span>
<span class="line"></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#89DDFF;font-style:italic;">if</span><span style="color:#A6ACCD;">()</span><span style="color:#89DDFF;">{</span></span>
<span class="line"></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#89DDFF;font-style:italic;">if</span><span style="color:#A6ACCD;">()</span><span style="color:#89DDFF;">{</span></span>
<span class="line"></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">}</span></span>
<span class="line"></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br></div></div><ul><li><p>switch case格式：</p><ul><li>表达式绝对等于对应的值时，执行对应的语句，break跳出</li><li>break跳出当前条件，如果没有break，不判断下一个条件是否满足，直接进入，这叫做穿越</li><li>default中不增加break</li></ul><div class="language-JavaScript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">JavaScript</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;font-style:italic;">switch</span><span style="color:#A6ACCD;"> (表达式) </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#A6ACCD;">     </span><span style="color:#89DDFF;font-style:italic;">case</span><span style="color:#A6ACCD;"> 值1</span><span style="color:#89DDFF;">:</span></span>
<span class="line"><span style="color:#A6ACCD;">         </span><span style="color:#89DDFF;font-style:italic;">break</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">     </span><span style="color:#89DDFF;font-style:italic;">case</span><span style="color:#A6ACCD;"> 值2</span><span style="color:#89DDFF;">:</span></span>
<span class="line"><span style="color:#A6ACCD;">         </span><span style="color:#89DDFF;font-style:italic;">break</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">     </span><span style="color:#89DDFF;font-style:italic;">case</span><span style="color:#A6ACCD;"> 值3</span><span style="color:#89DDFF;">:</span></span>
<span class="line"><span style="color:#A6ACCD;">         </span><span style="color:#89DDFF;font-style:italic;">break</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">     </span><span style="color:#89DDFF;font-style:italic;">case</span><span style="color:#A6ACCD;"> 值4</span><span style="color:#89DDFF;">:</span></span>
<span class="line"><span style="color:#A6ACCD;">         </span><span style="color:#89DDFF;font-style:italic;">break</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">     </span><span style="color:#89DDFF;font-style:italic;">default</span><span style="color:#89DDFF;">:</span></span>
<span class="line"></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">}</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br></div></div><div class="language-JavaScript line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">JavaScript</span><pre class="shiki material-palenight"><code><span class="line"><span style="color:#89DDFF;"> </span><span style="color:#676E95;font-style:italic;">// 举个例子</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">=</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#89DDFF;font-style:italic;">switch</span><span style="color:#A6ACCD;">(a)</span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#89DDFF;font-style:italic;">case</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">:</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#89DDFF;font-style:italic;">break</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">        a</span><span style="color:#89DDFF;">===</span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">||</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">===</span><span style="color:#F78C6C;">4</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#89DDFF;font-style:italic;">case</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">:</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#89DDFF;font-style:italic;">case</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">4</span><span style="color:#89DDFF;">:</span></span>
<span class="line"><span style="color:#A6ACCD;">        console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">aaa</span><span style="color:#89DDFF;">&quot;</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#89DDFF;font-style:italic;">break</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#89DDFF;">        </span><span style="color:#676E95;font-style:italic;">//穿越叠加</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#89DDFF;font-style:italic;">case</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">5</span><span style="color:#89DDFF;">:</span></span>
<span class="line"><span style="color:#A6ACCD;">        console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">a</span><span style="color:#89DDFF;">&quot;</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#89DDFF;font-style:italic;">case</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">6</span><span style="color:#89DDFF;">:</span></span>
<span class="line"><span style="color:#A6ACCD;">        console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">b</span><span style="color:#89DDFF;">&quot;</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#89DDFF;font-style:italic;">break</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#89DDFF;font-style:italic;">default</span><span style="color:#89DDFF;">:</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br></div></div></li></ul></li></ul></div></div></main><!--[--><!--]--><footer class="VPDocFooter" data-v-cfb513e0 data-v-21f75714><!----><div class="prev-next" data-v-21f75714><div class="pager" data-v-21f75714><!----></div><div class="pager" data-v-21f75714><a class="pager-link next" href="/docs/frontend/html/" data-v-21f75714><span class="desc" data-v-21f75714>Next page</span><span class="title" data-v-21f75714>html基础</span></a></div></div></footer><!--[--><!--]--></div></div></div></div></div><footer class="VPFooter has-sidebar" data-v-5211c0b1 data-v-9f24cc86><div class="container" data-v-9f24cc86><p class="message" data-v-9f24cc86>Released under the MIT License.</p><p class="copyright" data-v-9f24cc86>Copyright © 2019-present Evan You</p></div></footer><!--[--><!--]--></div></div>
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